|Publication number||US7321706 B2|
|Application number||US 11/295,331|
|Publication date||Jan 22, 2008|
|Filing date||Dec 5, 2005|
|Priority date||Dec 6, 2004|
|Also published as||DE502004005225D1, EP1666944A1, EP1666944B1, US20060127000|
|Publication number||11295331, 295331, US 7321706 B2, US 7321706B2, US-B2-7321706, US7321706 B2, US7321706B2|
|Original Assignee||Toptica Photonics Ag|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (14), Non-Patent Citations (1), Referenced by (2), Classifications (8), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Applicant claims priority under 35 U.S.C. §119 of European Application No. 04 028 837.5 filed Dec. 6, 2004.
1. Field of the Invention
The present invention relates to a fiber coupler for coupling light into an optical fiber and/or coupling light out of the fiber. The fiber coupler has two holder elements, namely a fiber holder for holding the fiber, and a lens holder for holding a focusing lens, whereby the holder elements are adjustable in the axial and transversal direction, respectively. Such fiber couplers are needed, among other things, in the sector of research, for optical experiments, and in the field of telecommunications technology, for systems for optical signal transmission.
2. The Prior Art
High requirements with regard to the precision of the positioning of the fiber end relative to the focusing lens are set for fiber couplers for coupling a free light beam into an optical fiber and for coupling light out of the fiber. Usual so-called single mode fibers have a mode field diameter of only a few micrometers. In the case of single mode fibers for a light wavelength of 780 nm, for example, the mode field diameter is only 4 μm. To couple a free light beam into such a fiber, it must therefore be possible to position the focusing lens to a precision of a few micrometers, along the optical axis. Only in this way can optimal efficiency be achieved when coupling in. A tolerance of 10 μm already reduces the efficiency of the coupling by 10%. The efficiency of the coupling is even more sensitively dependent on the transversal positioning relative to the fiber end. A deviation from the optimal position of only one micrometer in the transversal direction reduces the efficiency of the coupling by 20%.
A fiber coupler of the type stated initially is previously known from U.S. Pat. No. 5,282,393 A, for example. In the case of the previously known coupler, transversal and axial setting members, respectively, are provided to adjust the holder elements for the fiber and the lens, respectively. These members essentially consist of threaded rods that are guided in corresponding threaded bores of a base element. In this previously known coupler, the setting member provided for axial adjustment of the focusing lens along the optical axis consists of three threaded rods having screws guided on them. These screws are synchronously turned by means of a gear mechanism, in order to thereby allow linear movement of the focusing lens along the optical axis.
It is a disadvantage of the aforementioned fiber coupler that it consists of a plurality of mechanical components for the various setting members, which must be produced with the greatest precision. For this reason, the previously known fiber coupler is extremely expensive in its production. It is a further disadvantage that the gear mechanism described above can hardly be produced with sufficient precision for the axial adjustment of the focusing lens, in order to satisfy the requirements for fiber couplers used with single mode fibers, as mentioned above. Another disadvantage results from the complicated mechanical design of the previously known fiber coupler. It is a disadvantage that the structure of the coupler is not very compact. Finally, another disadvantage is the insufficient precision in the adjustment of the lens or the fiber end in the transversal direction, respectively, as well as the poor long-term stability of the adjustment.
Against this background, it is an object of the present invention to provide an improved fiber coupler, which allows adjustment of the focusing lens or the fiber, respectively, in the axial or transversal direction, respectively, with sufficient precision and long-term stability. In addition, the coupler should be compact in structure and inexpensive to produce.
These and other objects are accomplished according to the invention by providing a fiber coupler of the type stated initially, in which the holder elements are connected with a base body by way of at least one elastic monolithic joint, in each instance.
In the case of the fiber coupler according to the invention, the adjustability of the fiber or of the focusing lens, respectively, is based on the use of elastic monolithic joints. Because of the elastic properties of the monolithic joints, the setting mechanism needed for the fiber coupler can be implemented in particularly simple manner. Setting is simple because in order to make an adjustment, a force has to be exerted merely in one direction, counter to the elastic reset force of the joint. The reset force then automatically assures the long-term stability of the adjustment. The fiber coupler according to the invention has the advantage that the holder elements and the related base bodies can be produced in one piece with one another (monolithic) so that each holder element is integral with its associated base body. For this purpose, known electro-erosion methods, such as wire erosion, for example, can be used. The fiber coupler according to the invention therefore can be produced both cost-effectively and compactly.
In the fiber coupler according to the invention, it is practical if the monolithic joint of one holder element has a greater bending stiffness crosswise to the optical axis than parallel to it, while the monolithic joint of the other holder element has a greater bending stiffness parallel to the optical axis than orthogonal or vertical to it. In this way, the result is achieved that the holder elements for adjustment in the axial and transversal direction, respectively, are uncoupled from one another. The guidance of the movement of the individual holder elements that is required for the adjustment is achieved, in this connection, by means of the special configuration of the monolithic joints. Specifically, the monolithic joints have a significantly greater bending stiffness perpendicular to the desired movement direction than parallel to it, in each instance.
In order to adjust the focusing lens or the fiber, respectively, essentially parallel to the optical axis, it is practical if one of the holder elements is connected with the base body by way of a total of four monolithic joints and two lever arms, whereby the two lever arms are disposed in the manner of a parallelogram. By means of the arrangement in the shape of a parallelogram, an essentially linear movement is implemented. Tilting or turning of the focusing lens or of the fiber is avoided. All that occurs is an extremely slight parasitic arc movement of the holder element, but this movement has no noticeable effects if the stroke of the linear movement as a whole is limited.
For transverse adjustment, one holder element can be connected with the base body via at least two monolithic joints. Specifically, the connection is made so that the holder element is adjustable in two directions perpendicular to the optical axis. The arrangement of the monolithic elements can be selected so that the holder element is independently adjustable in two orthogonal directions perpendicular to the optical axis. It has been shown that plate joints are particularly suitable as monolithic joints for transversal adjustment. An arrangement of a total of three plate joints has proven to be practicable. In this connection, two of the plate joints are elastically stretchable in orthogonal directions perpendicular to the optical axis, specifically without elastic deflection of the third plate joint that is arranged in the center with reference to the two first plate joints.
In the fiber coupler according to the invention, an adjustment possibility in the axial or transversal direction, respectively, can be implemented in particularly simple manner. Such adjustment is made possible by an adjustment screw for fixing the position of the holder element relative to the base body, which screw engages on at least one of the holder elements. By means of this adjustment screw, a force counter to the elastic reset force of the monolithic joint acts on the corresponding holder element. Therefore, one adjustment screw is sufficient for adjustment for each adjustment direction, since this screw, interacting with the elastic properties of the monolithic joint, will determine the position of the holder element and, at the same time, fix it in place.
In the case of the fiber coupler according to the invention, as already explained, separate holder elements are used, which are adjustable independent of one another, either in the axial direction or in the transversal direction. One of the holder elements forms the fiber holder of the fiber coupler according to the invention, which serves to hold the fiber. The other holder element forms the lens holder for holding the focusing lens. In the fiber coupler according to the invention, it has proven to be particularly practical if the base body of the fiber holder can be fixed in place on the base body of the lens holder in different discrete angle positions with reference to the optical axis. This feature is important so that when using optical fibers that maintain polarization, the fiber can be disposed in accordance with the polarization direction. In practice, discrete angle steps of 45° with a precision adjustment possibility in the range of +/−4° are sufficient in this connection.
For the purpose of thermal insulation, it is practical to provide a housing for the fiber coupler according to the invention, which surrounds the holder elements and the related base bodies on all sides.
Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.
In the drawings, wherein similar reference characters denote similar elements throughout the several views:
Turning now in detail to the drawings,
Lens holder 1 is connected with a base body 3 by way of a total of four elastic monolithic or solid joints 2. Lens holder 1 is adjustable in linear manner in the axial direction, namely parallel to the optical axis 4. For this purpose, monolithic joints 2 have a clearly greater bending stiffness crosswise to optical axis 4 than parallel to it. In order to allow an essentially purely linear movement of the focusing lens, lens holder 1 is connected with base body 3 by way of the four monolithic joints 2 and two lever arms 5. In this connection, the two lever arms 5 are disposed in the manner of a parallelogram. This arrangement results in linear adjustability of the focusing lens, as indicated in
The special symmetrical arrangement of plate joints 8, 9, and 10 can be seen in
Although at least one embodiment has been shown and described, it is to be understood that many changes and modifications may be made therunto without departing from the spirit and socpe of the invention as defined in the appended claims.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8515228 *||Jun 23, 2009||Aug 20, 2013||Raytheon Canada Limited||Method and apparatus for accurately positioning an optical fiber end|
|US20100322585 *||Jun 23, 2009||Dec 23, 2010||Raytheon Company||Method and Apparatus for Accurately Positioning an Optical Fiber End|
|U.S. Classification||385/25, 385/93, 385/52, 385/33|
|International Classification||G02B6/36, G02B6/42|
|Feb 13, 2006||AS||Assignment|
Owner name: TOPTICA PHOTONICS AG, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HEIDEMANN, RAINER;REEL/FRAME:017563/0247
Effective date: 20051216
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